facial nerve by dr. apoorv
TRANSCRIPT
Facial nerve Apooorv Pandey.
Content Introduction Anatomy Clinical Examination Applied aspect
Facial nerve
Seventh CN- mixed nerve. Nerve of second brachial
arch Nerve of facial expression.
The facial nerve (CN VII) – motor + sensory
Parasympathetic secretory fibers submandibular, sublingual salivary glands lacrimal gland mucous membranes of Oral and nasal
cavities.
Sensory functions: Taste sensation (eardrum and external auditory
canal) sensation: the muscles it supplies
Infranuclear
Nuclear
Four components
Supranuclear
Pyramidal and extrapyramida
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ANATOMY
SUPRANUCLEAR ANATOMY
Has specific areas on the cerebral cortex.
Facial pyramidal fibers begin
It is represented according to the part it supplies on the face.
Path of voluntary facial expressions (Pyramidal)
Contralateral precentral gyrus are carried through corticobulbar tract (pyramidal)
Internal Capsule
Midbrain
Cross over to the opposite side
Motor Facial nerve nucleus in Pons.
DeJong's The Neurologic Examination, 6th Edition
Facial Nerve has 4 nuclei (lower pons)
1. Motor nucleus
2. Sup salivolacrimatory nucleus (parasympathetic)
3. Nucleus of tractus solitarius (gustatory)
4. Spinal tract nucleus (sensory)
Nuclear / Intra-axial Anatomy
DeJong's The Neurologic Examination, 6th Edition
Motor nucleus fibres
Ventrolateral pontine tegmentum
Floor of fourth ventricle forming
facial colliculus Fibers then course anterolaterally to exit lateral
brainstem at pontomedullary junction
Sup salivolacrimatory nucleus (parasympathetic)Nucleus of tractus solitarius (gustatory)Spinal tract nucleus (sensory)
NERVOUS INTERMEDIUS
DeJong's The Neurologic Examination, 6th Edition
The facial nerve leaves the brainstem in two roots
MOTOR ROOT (70%)
NERVOUS INTERMEDIUS (30%)
Extra-axial course
Emerge from lateral brainstem at root exit zone on pontomedullary junction just caudal to the roots of CN V
Cerebellopontine angle (CPA) cistern
DeJong's The Neurologic Examination, 6th Edition
Cisternal segment
Has 2 roots at the exit Larger motor root anteriorly Smaller sensory nervus intermedius posteriorly
CN8 exits brainstem posterior to CNVII
These nerves resemble the nerve roots of the spinal cord in that
they are devoid of epineurium but covered in piamater and
bathed in cerebrospinal fluid.Diagnostic and imaging anatomyHarnsberger
Intrapetrous course of the facial nerve has two portions:
(a) in the internal auditory canal (b) in the facial canal or Fallopean
aqueduct
The internal auditory segment is 7 to 8 mm in length
At the entrance to the internal auditory canal (IAC)
The facial nerve at this point lies in
close proximity to the anterior inferior cerebellar artery
(AICA)
In its course through the facial canal the nerve has four segments:
1) Labyrinthine II) Horizontal or tympanicIII) PyramidalIV) Mastoid
Bell’s Palsy: Diagnosis and Management JEFFREY D. TIEMSTRA, MD, and NANDINI KHATKHATE, MD University of Illinois at Chicago College of Medicine, Chicago, Illinois
The labyrinthine segment lies laterally between the cochlea and vestibule,toward the medial wall of the tympanic cavity
It extends from the internal auditory canal to the geniculate ganglion. (3–5 mm)
The nerve turns abruptly and runs horizontally for about 1 cm (horizontal or tympanic segment)
Turns backward and arches downward behind the tympanic cavity.
Extends from the geniculate ganglion to the second turn of the facial nerve
External genu & geniculate ganglion
The tympanic nerve segment is covered by a thin bony sheath.
The pyramidal segment joins the horizontal and mastoid segments, and gives off the branch to the stapedius muscle.
The mastoid segment (13–15 mm)
extends from this point to the
stylomastoid foramen.
In the adult, it is protected laterally by the mastoid tip, tympanic ring and mandibular ramus.
Whereas in children younger than 2 years it is relatively superficial.
Postauricular incisions in this younger population must be carefully planned because the trunk of the facial nerve is a subcutaneous structure at this level.
Pesanserinus
SensoryGreater sup. petrosal
nerveChorda tympani
MotorNerve to stapediusPosterior auricularNerve to DiagastricNerve to stylohyoidMuscles of facial
expression
Branches
After exiting the stylomastoid foramen, the facial nerve gives off branches to
The posterior auricular The posterior belly of digastric The stylohyoid
Post auricular branch Ascends btw EAM and mastoid Divides into auricular and occipital
branches
Digastric branch Posterior belly of digastric
Stylohyoid branch Stylohyoid muscle
Final Innervation
Innervates the muscles of facial expression.
General Somatic Efferents
Parasympathetic fibres
Temporal bone
via the petrosal foramen
Enters middle cranial fossa
via the foramen lacerum
And reaches the base of medial pterygoid plate
Meet sympathetic fibers of deep petrosal nerve.
The parasympathetic and sympathetic fibers together make up the nerve of the pterygoid canal
Greater Superficial Petrosal Nerve
Upon exiting the pterygoid canal, pre-ganglionic parasympathetic fibers of CN VII synapse in the pterygopalatine ganglion
(which is suspended from the fibers of the maxillary division of the trigeminal nerve (V2) in the
pterygopalatine fossa.)
Post-ganglionic parasympathetic the lacrimal gland (via the lacrimal
nerve) mucous membranes of the nasal and
oral pharynx
Special Visceral Afferents or Sensations
Corda Tympani Course
The fibers pass through the middle ear in close relationship with the tympanic membrane and exit the base of the skull to enter the inferotemporal fossa.
In the inferotemporal fossa the chorda tympani joins the lingual branch of the mandibular division of CN V (V3).
Pre-ganglionic fibers synapse in the submandibular ganglion
Post-ganglionic fibers then enter the submandibular gland
General Somatic Afferents
Applied aspect
(1829): THE DISCOVERY
OF THE NERVE OF FACIAL EXPRESSION
Sir Charles Bell (1829)
3 cases of facial paralysis due to facial nerve trauma.
Causes of nerve palsy
Clinical Examination of the facial nerve
Motor
Frontalis, Corrugator Supercilii Orbicularis oculi Buccinator Orbicularis Oris Platysma
Sensory
Evaluation of taste on the anterior two-thirds of the tongue.
Four fundamental tastes (sweet, sour, salty and bitter)
and asymmetries documented.
Reflex and Parasympathetic Function
Corneal Reflex Lacrimation
Salivation
Other important tests
1. Schirmer's Tear test
2. Nerve conduction and Potential
Studies
3. CT / MRI
Inflammatory facial nerve lesions can be demonstrated by MRI after gadolinium contrast administration.
Otogenic and traumatic facial paralysis should always be evaluated by thin-slice bone-window CT scanning of the temporal bone.
Testing facial nerve function
90% of nerve disorder occurs along the nerves intra temporal course
Electro diagnosis – testing degree of distal axonal degeneration
Topognosis – testing function of accessory branches
Facial nerve tests:
Topognosis - lacrimation, stapedial reflex, salivary flow, taste
CT- to rule out trauma to the nerve
Prognosis – Electromyography (EMG) Electrical Nuro Graphy (ENoG)
Diagnostic – Blink reflex, EMG, ENoG
Electro diagnostic testing
EMG-electromyography Is a electro physiologic test It measures electrical response
1. During needle insertion2. At rest
3. During volitional movement
Nerve conduction time:
Nerve stimulated near the foramen and record one of the facial muscle group
Latency for each action potential is defined as the time between onset of stimulus and onset of response
Cortical innervation of left
face
Upper half: BiLateral
Lower Half: Predominantly contralateral
Left
Lower Motor Neuron (LMN) Lesion
Clinical Examination
Upper Motor Neuron (UMN) Palsy
Facial ParalysisUPPER MOTOR NEURON LOWER MOTOR NEURON
Lesions is above the pons. Lesions is in the pons or in the pathway from pons to its exit.
Patient can make furrows on looking upwards
Furrows are absent on looking upwards of the affected side of face.
Lower part of the face is involved on the opposite side of the lesion.
The whole face and forehead involved on the same side of the lesion.
Isolated involment of this type is rare.
Isolated involment of this type is common.
It is invariably associated with hemiplegia .
It may be associated with hemiplegia .
GRADING
Dr John W. House and Dr Derald E. Brackmann, otolaryngologists in Los Angeles,
who first described the system in 1985.
Vrabec JT, Backous DD, Djalilian HR, et al. (April 2009). "Facial Nerve Grading System 2.0". Otolaryngol Head Neck Surg
Localization of Lesions Affecting Cranial Nerve VII
Supranuclear Lesions (Central Facial Palsy)
Nuclear and Fascicular Lesions (Pontine Lesions)
Peripheral Facial Nerve Palsy
Nuclear Lesions May affect either the nucleus of the facial nerve or its
intrapontine axons
Ipsilateral Facial palsy with
Abducens fascicle or nucleus
Paramedian Pontine Reticular Formation
(PPRF)
(paralysis of conjugate gaze to the psilateral side)
Corticospinal tract (contralateral hemiplegia)
Abducens fascicle or nucleus
PERIPHERAL LESIONS
Lower motor lesion of Facial nerve
• Palsy +loss of taste sensation – in the
canal
• Palsy +loss of taste +hyperacusis – just
after entrance into the canal
• All the above + loss of hearing – at the
internal auditory meatus
• All the above + lateral rectus damage –
cerebo potine angle involvement Bell’s
palsy.
Millard-Gubler Syndrome
Lesion located in the ventral pons that destroys the fascicles of the facial and
abducens nerves and the corticospinal tract
Ipsilateral peripheral-type facial paralysis
Ipsilateral lateral rectus paralysis
(diplopia with failure to abduct
the ipsilateral eye)
Contralateral hemiplegia
Foville Syndrome
Lesion located in the pontine tegmentum that destroys the fascicle of the facial nerve, the PPRF, and the corticospinal tract.
Ipsilateral peripheral-type facial paralysis
Paralysis of conjugate gaze to the side of the lesion
Contralateral hemiplegia
Möbius syndrome
Möbius syndrome results from the underdevelopment of the VI and VII cranial nerves.
Loss of facial expressions and horizontal gaze.
EXTRAPYRAMIDAL SYSTEM
Consist of basal ganglia and the descending motor projections other than the fibers of the pyramid or cortico-bulbar tracts.
Extrapyramidal system, involves diffuse axonal connections between multiple regions including the basal ganglia, hypothalamus, and motor cortex.
The extrapyramidal system is capable of producing involuntary facial movements (absence of major pyramidal pathways)
A dissociation between voluntary facial movements (volitional facial palsy) and emotional facial movements (emotional or mimetic facial palsy)
Important points during Embryonic Development
• 7th cranial nerve is first identifiable at the end of 3rd week
• Important steps in facial nerve development occurs throughout gestation and the nerve is not fully developed until appx 4yrs after birth.
• Because the cell collection also gives rise to the 8th cranial (acoustic) nerve, it is referred to as the facioacoustic cranial primordium or crest.
During its development the facial and Vestibulochochlear nerve are not distinguishable till the 37th day of the embryonic life.
The facial nerve is the nerve of the second branchial arch and its branch, chorda tympanic develops as the nerve to the first branchial arch during the early embryonic period.
6th an 7th cranial nerve motor nuclei lie in close approximation
Congenital Mobius syndrome Acquired inflammatory /vascular / neoplastic
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